Taming your Fox Hawk 60 engine

Project #7 - Taming your Hawk .60


Bore: .907
Stroke: .937
Disp: .604
Weight: 15oz
13,500 with pattern carb. and narrow blade 11-7 prop. 23,000 with large throat carb. and 9-7 racing type prop.

Powerful as well as attractive, the Hawk was Duke's first schnuerle ported .60. Unusual features included a cylinder section made with integral steel fins and an ultra-hard piston made from low expansion aluminum. With an expansion rate comparable to that of iron, the piston could be fit much closer, however, it seems that, on some examples, this was pushed a bit too far. Although there was tremendous potential here, the Hawk also exhibited a few problems that kept it from becoming as popular as it could have been. The engine can be modified to overcome these, however, the modifications are such that proper tools and machining skills are required to accomplish them. For those of you with the facilities, and skills, the following modifications will allow your Hawk .60 to reveal it's true, and considerable, potential.

The Problems:
There are two problems that must be taken care care of to smarten up the Hawk. These are: excessive compression in general, and, on some engines, an overly tight fit.

Fixing the Compression Problem:
The Hawk was the first of numerous Fox engines over the years in which the compression was, in our opinion, just too high for friendly operation when using typical sport fuels (10-15% nitro). Although Duke claimed the engine would run well on fuel containing up to 25% nitro, we never found this to be true. Even on lower nitro fuels, these engines could be inconsistent, very finicky to adjust, run hot, and flameout unexpectedly. We found that lowering the compression was the only way to cure this. The addition of shims alone was not adequate, and machine work to the head itself was also required. Material is removed in a cone-shaped pattern as indicated by the shaded area in the diagram below. Be warned that spare parts are no longer available if you ruin the head. Proceed with care!

If you interested in having this modification done but cannot manage it yourself, we have a recommended source for custom machine work..

(Click on picture for larger view)

Important Note: This modification will eliminate about half of the glow plug threads. After the modification, use short reach plugs!
Here's a picture of a stock and modified head

In addition to the head modification, you will require two head shims made from .010" stock. If your flying site is at a high elevation and/or you keep the nitro content below 10%, you may get away without the shims. You can experiment a bit here.

Fixing the Fit Problem:
The following quote from the Owners Manual will give you an idea of what the problem is:

"In the interests of good compression and long life we have fitted your Hawk as tight as we dare. In the event yours is fit too close and you have trouble with the piston seizing (engine stops abruptly on lean).....return it to us and state your problem and we will hone it out at no charge."

Since this engine has been out of production for decades, it is unlikely that the offer from Fox would still apply, free or otherwise. Of the two samples we have in our personal collection one exhibited the seizing problem, but we had the ability to hone it, which cured the problem. If you also have this problem you will likely need to do the same.